Process for the manufacture of cellulose acetate



v Hydrochloric acidahas been'recommended' l atented Sept. 20, 1932 .,UNITEDfSTAT SPATE L j OFFICE? SAMUEL E. snnrrann, or ROCHESTER, NEW YORK, AssIGNonTo' EASTMAN KODAK COMPANY, or ROCHESTER, NEW yonmnconrona'rron or NnwYoRK a .rnocnssron THEMANUFAGTURE-OF CELLULOSE ACETATE i No Drawing.

perature of approximately 40 C. until a cellulose tri-acetate. is obtained. The cat- 'alysts-which have been recommended for this purpose have been legion but it appears that those Which are'most successful are the min eral acid. catalysts including, for example,

sulfuricacid, phosphoriclacid, etc.

iii-the past for this purpose as in British Pat- "ent 2026 B of 1907, in. which the acetylating reaction is carried onfin the usual acetylation'solution'containing an aqueous solution of hydrochloric acid. The'quality of the cellulose acetateresulting from this "reaction is not therein disclosed. It is wellknown, however, to those familiar with this art-that such a reaction will produce acellulose acetate,-the moleculeof which. is considerably degraded, i. c. it is believed that such reactions :break up the. long cellulose molecule which results in a cellulose acetate having-little or 110 value. This; is readily evidencedin the films, which are formed by spreading a solution of the ester on a suitable surface, and evaporating therefrom. the sol- "vent, in that these films are exceedlngly brittle; The viscosity of such acetates,"when hydrolized to acetone solubility and dissolved in an acetone. solution, is very low,

which is another indicationoftheirdegrada- The object lulose acetate whereby an: undegraded acel .l'ulose acetate of a high degree of uniformity islobtained; Other objects will hereinafter appear. r I have found that by treatingcellulose in a reaction mixture with-hydrochloric acid and Y a gsuitablereducing substance that the appreciable amounts in a sohition offhydrochloric acldcontaining any. moisture. This 7 following formula:

of A the present invention is l to provide a method for the use of hydrochloric, acid as a catalystin the-production of cel- Application'iile d .Tu1y'15,1929;' Serial nmcvasw.

above described deleterious actibii'oithis i catalystis greatly inhibited. Infthe presence of; -such areducing substance inthe re v action mixtures a uniform reaction takes place, theusual drastic elfectiof the hydrochloric acid which results when hydrochloric acid is used withoutmyreolucing substance beingabsent.

' I have found good reasons to attribute the drastic action'of the hydrochloric acid as a the Water present, notably among these products is hypochlorous acid which is present in oxidation product-0f Y hydrochloric acid is readily formed by photochemically induced autoxidation which maybe representedlbythe is notessential to the carrying out of this t st catalyst upon the oxidationi products which invention but may more clearly bring out the reasoningjby which the results herein obtained were: arrived at, nor does-this 'dis cuss'ion preclude the possibility that higheroxidation products,as perchloric acid, are also found to'some-extent; ,There are several. re-

actionswhich could be used as evidence of the undue-oxidizing power; of hydrochloric acid solution, of which one is the oxidation -ofcolloidal silver to silver-chloride, another the oxidation of sulfides and. sulfuretted hydrogen.

and to 'confine its action primarily to its acidic; function, I find itsuflicient to add quite-small quantities of certain reducing substances to the hydrochloric .acid' solution which bufi'er th'e'solution against oxidation, The nature 1 of these reducing agents, as they maybe called, will,'of course," be regulated by To'prevent the formation of theseoxidation reactions in hydrochloric acid solutions a .the typeof solution lI'LWhlClI theyigare-tobe used. I have found: that-the following-sub stances "are: suitable for thispurposef-but ;it v

is generally easy to select numerous other suitable examples other than those hereinbes low specified. Sulfurous acid (S arseni- "acetate--toan ac'etatefha-ving' the desired ous acid (AS O ),StaI1IlOUS oxide, antimonous oxide, hypophosphorous acid (HPO may be mentioned as inorganic componds as buflfers for this purpose while among the organic 'reducingsubstances which I have found suit- ;able ior use in various solutions .are m'annose, lactose, glucose, phenol, polyphenols, hydroquinone, amino-phenols and partlcularly suitable for the prevention of the degradation of the-cellulose molecule whatevermay be the cause of this action of the hydrochloric acid when used" alone. In hydrolyzingmixtures, for the deacetylation of the cellulose solubility, consisting of acetic acid, water and hydrochloric acid it is likewise suitable.- The small amounts of sulfuric acid] which ,are eventually foifmed by th e oxi'da'tion of the sulfurous acid aremu'ch" less powerful than the oxidizingside protilucfts -re'sulting from the hydrochloric acid r i 1 1 It is, of course, understood thatithe-above example ofthe use of sulfurous acid is merely indicative of other reducing agents which may be used in any of the well-known types of acetylating reaction mixtures in which hydrochloric acid may be used as 'a catalyst;

it being borne in mind that the reducing sub-' stance used must be compatible'with; the ingredients of the solution and in'n o way'break 'downthe other ingredients therein.

Under the usual acetylating conditions it is advisable to use in the order'of 1/100 per cent to 5 per cent of the hydrochloric'acid present :ofa reducer; This amount surprisingly reduce's the drastic action of the hydrochloric acid catalyst and'ther'eby allows the reaction to proceed more uniformly whereby anjundegraded product is obtained having an excep-- tionally high quality. This is shown by a 'lowercopper reducingpowerof the cellulosic products and a much less reduction inviscos- 'ity for equal times of reaction and also solutions'coated from a hydrolyzed-solution of the acetate, result infilms having a gooddegree' 'of flexibility.

Various equivalents may be 'used as a reducing substance to bufie'r the autoxidation of thehydrochloricacid without in any way departing from his invention or sacrificing any of thead'vantages; derived therefrom. These reducingsubstances maylikewise be used in all the types of acetylating mixtures in common use in which the acidic action of the hydrochloricj'acid is more desirable than its oxidizing action and likewise when it is desirable to inhibit the drastic attack on the cellulose molecule by the untreated hydrochloric acid catalyst. v

Having thus described my invention, what I claim as new and desire to secure by Letters Pa t i 1. The proces's'ior the manufacture of organic esters ofcellulose which. comprises conducting the reaction ina'liquid bath containjing: hydrochloric acid and a reducing substance which bulie'rs the hydrochloric acid against autoxidation.

" 2. The process for the-manufacture of or- 1 ganic esters of "cellulose which comprises acylatlng cellulose in a liquid bath containing hyrochloric-acidand a reducing substance which bufiers the hydrochloric acid against autoxidation. V f 7 3. The process for the manufactureof cellulose acetatewhi'ch comprises acetylating .-cellulose inaliquid'bath containing hydrochloric acid and a reducing substance'which bufiers the hydrochloric acid against autoxidation'. a p

i; The process for themanufacture of cellulose acetate which comprises a cetyla-ting cellulose in a liquid bath containing hydrochlorio acidandl 100% .t'o'5% of sulphurous acid based upon the hydrochloric acid present.

-5. The process iorthe manufacture of or.-

-ganic .esters o f cellulosewhich comprises conducting the reaction in-aliquidbath contain- I ling hydrochloric acidand 1 /100 to 5% of a reducing substance :based chloric. acid present. I I

6.". The process for V ganrc esters oi cellulose which comprises acyl- 'ating cellulose inia liquid;bathvcontaining' hydrochloric acid and 1/100 to 5% of a re- :ducing substance based upon the hydrochloric acid present. r 5 i 7. The processior the manufacture of orthemanufactureof or? upon the hydro- "ganicest ers of cellulose which comprise's'reacting'on cellulose with ali'quid bath containing hydrochloric acid as a catalyst and a reducing substancexwhich" buffers the hydrochloricacid against autoxidation.

' 8. The process -for' the ma nu'facture z of cellulose acetate which. comprises pre-treating, acylatiiig anjd hydrolyzin'g' cellulose T in liquid baths containing hydrochloric'acid' and a reducing substance which bufiers-thehydro- V chloric" acid against autoxidation:

lose acetate which comprises acetylating cellulose'in ab'ath containing hydrochloric-acid f 9.""A process ior the manufacture of celluf and f 100%fto=5. ;er hydroquinoriebased 1 upon the hydrochloric acid present. i

' Signed at Rochester,"NewIYork,thiszsth day oi:'= July,'-1929. Y 4

i I E. SHEPPARD; 

